"Oh, diamond dust. She fell underground."
"I guess we'll just have to drill through the planet until we hit something."

There are two possibilities:

1. Yellow Diamond told them to capture the leader of the Earth Expedition, and they wrongly assumed she meant Jasper instead of Peridot, because Rubies are idiots, OR

2. Jasper is being blamed for Peridot's rebellion and the mission's failure, so Homeworld has declared her an outlaw.